Engine exhaust emission regulations are becoming increasingly restrictive. One way to meet emission standards is to rate shape the quantity and timing of the fuel injected into the combustion chamber to match the engine cycle. Effective rate shaping may result in reduced levels of particulate and oxides of nitrogen in the engine exhaust. Further, effective rate shaping that injects fuel slower during the early phase of the combustion process results in less engine noise.
Existing rate shaping techniques attempt to control injection rates by making various modifications to the injector nozzle assembly. The nozzle assembly rate shaping technologies create undesirable effects such as poor spray patterns resulting in less than optimal fuel economy and particulates. Although these existing rate shaping techniques have been employed in some applications, there is a need for a rate shaping technique that allows more precise rate shaping than the existing modified injector nozzle assemblies.